Abstract
The efficiency requirements for hydraulic pumps applied in automatic transmissions in future generations of automobiles will increase continuously. In addition, the pumps must be able to cope with multiphase flows to a certain extent. Given this background, a balanced vane pump (BVP), an internal gear pump (IGP) and a three-dimensional geared tumbling multi chamber (TMC) pump are analyzed and compared by a computational fluid dynamics (CFD) approach with ANSYS CFX and TwinMesh. Furthermore, test bench measurements are conducted to obtain experimental data to validate the numerical results. The obtained numerical results show a reasonable agreement with the experimental data. In the first CFD setup, the conveying characteristics of the pumps with pure oil regarding volumetric efficiencies, cavitation onset and pressure ripple are compared. Both the IGP and the BVP show high volumetric efficiencies and low pressure ripples whereas the TMC shows a weaker performance regarding these objectives. In the second CFD setup, an oil-bubbly air multiphase flow with different inlet volume fractions (IGVF) is investigated. It can be shown that free air changes the pumping characteristics significantly by increasing pressure and mass flow ripple and diminishing the volumetric efficiency as well as the required driving torque. The compression ratios of the pumps appear to be an important parameter that determines how the multiphase flow is handled regarding pressure and mass flow ripple. Overall, the BVP and the IGP show both a similar strong performance with and without free air. In the current development state, the TMC pump shows an inferior performance because of its lower compression ratio and therefore needs further optimization.
Highlights
In the last few years and in the decades to come the automotive industry worldwide faces a great transformation
A numerical study to compare three different positive displacement pumps regarding the application in future automatic transmission system was presented in this paper
A distinctively higher deviation between numerical and experimental results could be observed for the tumbling multi chamber (TMC) pump, as the computational fluid dynamics (CFD) results overpredicted the volumetric efficiency
Summary
In the last few years and in the decades to come the automotive industry worldwide faces a great transformation. Continuous variable transmissions (CVT) and dual clutch transmissions (DCT) became more and more popular in the last decades [2] All these transmission systems have in common that they require a hydraulic circuit to operate. There are electrical powertrains that include a two-speed automatic transmission for efficiency reasons or to achieve higher top speeds and starting torques [5] These systems likewise require a hydraulic oil circuit to operate. Overall, this means that despite the ongoing transformation towards electrical powertrains, automatic transmissions will still be present for many years and need to be further improved and developed. The respective hydraulic pumps need to be further developed and optimized, as they are essential for the function of the systems
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